Recent results from the COMPASS hadron program

Technische Universität München, James-Franck-Straße, 85748 Garching

^a e-mail: sebastian.uhl@mytum.de
^b The author acknowledges financial support by the German Bundesministerium für Bildung und Forschung (BMBF), by the Maier-Leibnitz- Laboratorium der Universität und der Technischen Universität München, and by the DFG Cluster of Excellence “Origin and Structure of the Universe” (Exc153).

Published online: 24 November 2014

Abstract

COMPASS is a fixed-target experiment aimed to study the structure and dynamics of hadrons. Using a 190 GeV/c pion beam, the spectrum of light mesons is studied at four-momentum transfers squared to the target between 0:1 and 1:0 GeV²/c². The flagship channel is the diffractive production of π⁻π⁻π⁺ final states for which COMPASS has recorded the world’s largest data sample. The determination of properties of known resonances, and the search for new states is also pursued in the π⁻π⁰π⁰ final state, and in centrally produced systems. The structure of light mesons is studied in Primakoff reactions at lowest four-momentum transfers. Using these processes, the polarizability of the pion, the radiative width of the a₂ (1320) and, for the first time, that of the π₂ (1670) have been measured.